Heat treatment and mechanical properties of low-carbon steel with dual-phase microstructure

Purpose: The aim of the paper is to design heat treatment conditions of dual-phase steel and to determine their influence on the structure and mechanical properties of steel. Design/methodology/approach: The heat treatment of the C-Mn steel in order to obtain a dual-phase ferritic – martensitic structure of desirable phase fractions was realized. To investigate the influence of heat treatment parameters on the structure light and transmission electron microscopy methods were used. Mechanical properties were determined by means of tensile test. A strain hardening exponent as a function of true strain was evaluated, too. Findings: It was found that an initial structure influences essentially the morphology of martensite in an obtained dual-phase structure. It can occur as a network, fine fibres or islands in a ferritic matrix of high dislocation density in the vicinity of diffusionless transformation products of austenite. The best combination of strength and ductile properties has a steel with the martensite in a form of fine fibres. Research limitations/implications: Investigations concerning using the thermomechanical treatment to obtain a ferritic – martensitic structure of steel are required. Practical implications: The established heat treatment conditions can be useful for manufacturing dualphase structure sheets characterized by high strength and ductile properties as well as a good suitability for metalforming operations. Originality/value: The relationship between the initial structure and martensite morphology in dual-phase steels was specified.